5 Answers
5

Monsters are more vulnerable to silver swords, while humanoids (humans, elves and dwarves) are more vulnerable to steel swords. If you use the wrong sword type you will make far less damage. Always use the silver sword against monsters and the steel sword against humanoids.

Same reason as why you had to use it in the first instalment of the game: it makes monster fights easier. You can play it the hard way and try hacking away at everything with your long sword but not everybody wants to subject themselves to such masochistic enjoyments.

"Steel for men, Silver for monsters. Sadly, I have used both." -Geralt of Rivia.

The silver blade is the most effective against monsters, but does minimal damage to men, elves, and dwarves.

The Steel blade can be uprgraded by meteorite chuncks, and is mainly used for humanoids. During my time playing, I noticed it was also more effective against woodland creatures(Wolves), than the silver sword.

It makes fighting monsters easier, because many of the beings that appearing in the conjunction are weak or vulnerable to silver.

It doesn't really make sense that no one else uses this knowledge, other than Witchers - especially because in the world literally around every corner there is a monster of some kind, often almost next to settlements.

Then again, Witchers are known to use their knowledge - so that they're not "just any other man with a sword". Additionally, we can probably assume that a) Silver swords are hard to make, due to the "soft" nature of silver (yes, I'm aware of the iron core bit), and b) rather expensive
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JeevaJul 7 at 10:11

Swords aren't easy to make, and it would be even more difficult making silver and iron work together for a pre-industrial blacksmith, especially because those metals have completely different properties; a conventional iron blacksmith for example wouldn't have any knowledge or muscle memory of working with silver and it would be difficult for him to work with it. It seems like it probably makes more sense for the village to pool their funds to hire a Witcher that actually knows what they're doing instead of forge a silver sword that no one can use correctly anyway.
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Lucas LeblancJul 7 at 15:12